1. Field of the Invention
This invention is directed toward solid phase synthetic methods for forming sulfur-linked disaccharides and oligosaccharides. In these methods, a saccharide or oligosaccharide bearing a protected thiol-group is immobilized onto a solid support at any position other than the protected thiol group. The thiol protecting group is then removed and optionally converted to its thiolate salt. The resulting thiol/thiolate is allowed to undergo nucleophilic saccharide addition to provide for a solid phase bound di- or oligosaccharide.
In a preferred embodiment, the nucleophilic saccharide addition reaction involves a saccharide or oligosaccharide group which has been activated at the desired point of linkage by introduction of a leaving group which is displaced by the thiol/thiolate to form a sulfide linkage.
In another preferred embodiment, the protected thiol group on the saccharide or oligosaccharide is located at the anomeric carbon atom of the reducing saccharide group.
References
The following publications, patents and patent applications are cited in this application as superscript numbers:
1 Hindsgaul, 1-Thiogalactose Derivatives, International Patent Application Publication No. WO 98/21221, published 22 May 1998. PA0 2 Witczak, et al., Thiosugars II, Carbohydrate Research, 301:167-175 (1997). PA0 3 L. X. Wand, N. Sakari and H. Kuzuhara, J. Chem. Soc. Perkin Trans., 1:1677-1682 (1990). PA0 4 L. A. Reed and L. Goodman, Carbohydr. Res., 94: 91-99 (1981). PA0 5 S. Mehta, J. S. Andrews, B. D. Jonston and B. M. Pinto, J. Am. Chem. Soc., 116: 1569-1570 (1994). PA0 6 Hindsgaul, Combinatorial Synthesis of Carbokydrate Libraries, International Patent Application Publication No. WO 98/22487 published May 28, 1998. PA0 7 F. Shafizadeh, R. H. Fumeaux and T. T. Stevenson, Carbohydrate Res., 71 (1979) 169-191. PA0 8 M. G. Essig, Carbohydr. Res., 156 (1986) 225-231. PA0 9 T. W. Greene and G. M. Wuts, Protecting Groups in Organic Synthesis, Second Edition, Wiley, N.Y., 1991. PA0 10 Gallop, et al., U.S. Pat. No. 5,525,734, for "Methods for Synthesizing Diverse Collections of Pyrrolidone Compounds", issued Jun. 11, 1996
2. State of the Art
Thiosugars, or 1-thioglycosides, have heretofore been disclosed for a variety of uses. For example, Hindsgaul.sup.1,6 discloses that certain thiogalactose derivatives are useful in blocking the binding of toxins, such as heat-labile enterotoxin or cholera toxin, to their receptors either in vivo or in vitro. Similarly, Witczak, et al. .sup.2,7 have disclosed thiosugars (both .alpha. and .beta. linked thiodisaccharides) as being useful as probes in enzyme-inhibition studies and as components of sugar antibiotics.
The synthesis of compounds having such thio linkages is generally more difficult than the corresponding ether linkages. For example, the sulfur atom in thiol groups is less electronegative than the oxygen atom in alcohols, and therefore has a lower affinity for protons. For this reason, the thiol group is typically deprotonated to the corresponding thiolate group (e.g., --S.sup.-) prior to alkylation.
In any event, solution phase synthesis of thio linked disaccharides has been achieved by several methods, such as S.sub.N 2-type reactions between thiolate anions and glycosyl halides.sup.3, displacement of a leaving group by a 1-thioglycopyranose.sup.4, and condensation of benzylated 1,6-anhydro-glucopyranose with a protected 4-thioglucopyranoside..sup.5 These conventional methods arc generally multi-step methods producing a variable yield of the desired product. Other methods of producing thiodisaccharides by Michael addition of sugar thiols to levolglucosenone are also known..sup.7,8
However, the above conventional means of forming thio di- or oligosaccharides require the formation of the thio di- or oligosaccharide in solution. This presents the difficulty of removing undesired side products and excess reagents without affecting the desired end product or reducing yield during purification.
A solid phase reaction for formation of a thio-linked saccharide compound would be particularly desirable because it would allow facile purification of the ultimate product, as well as of any intermediates produced during synthesis, without reducing overall yield. However, there apparently has been no reported methods for forming thio di- or oligosaccharides on a solid support.